The present invention generally relates to a control method and management method for a storage system that is accessed by a computer in a computer system and, more particularly, to a method for assigning storage areas of a nonvolatile memory built into the storage system and to a storage area management method.
The information that is handled by businesses and so forth has undergone an explosive increase in keeping with the deregulation of electronic document conversion and the conversion of procedures to electronic document format, as well as the increase in Internet business. In addition to an increase in such information, the amount of data stored in storage devices is increasing rapidly and leading to an increase in the scale of storage systems as a result of rising customer demand for the long-term archiving of recordings of corporate activities (transaction information and mail and so forth) in the form of data backups from one disk device to another disk device (Disk-to-Disk Backup) and audit handling.
Accordingly, there is a demand for simplification and increased efficiencies in the management of complex IT infrastructures at the same time as increased storage for the respective departments/respective systems in business information systems. In particular, expectations have increased for simplifying the management of storage devices and optimizing the total costs by using optimal storage in accordance with the value of data.
One method for reducing the management costs of large-scale storage systems includes the storage virtualization technology as disclosed in Japanese Application Laid Open No. 2005-11277. Japanese Application Laid Open No. 2005-11277 discloses a storage virtualization technology (referred to as an ‘external storage connection method’ hereinbelow) that connects a first storage system to one or more second storage systems and provides a higher level such as a host with a device (called a ‘logical device’ hereinbelow) that is provided to the host or the like by a second storage system as a logical device of the first storage system via the first storage system. When the first storage system receives an I/O request with respect to the logical device from the host, it is judged whether the access target device corresponds to either a logical device of the second storage system or a physical device such as a disk device in the first storage system and I/O requests are distributed to suitable access destinations in accordance with the result of this judgment.
In addition, one method for simplifying the storage system design includes a volume management technology that is capable of dynamic capacity expansion of the kind disclosed in Japanese Application Laid Open No. 2003-15915 (A volume capacity of which is expanded dynamically called an expansion volume hereinbelow). In Japanese Application Laid Open No. 2003-15915, during the definition of a logical device, a pool area is provided in a storage system instead of assigning a fixed physical storage area (HDD or the like) corresponding to a device capacity that is requested by the user and, when update access has been made to the logical device, a physical storage area of a prescribed amount is dynamically added from the pool area corresponding to the updated part. As a result, a large-capacity logical device can be introduced using a small physical storage area and the storage capacity design can be simplified.
On the other hand, as one method for reducing the introduction and running costs of a large-scale storage system that stores a large amount of data of the kind mentioned hereinabove, the storage mounting technology that adopts a nonvolatile memory such as the flash memory disclosed in Japanese Patent No. 3507132 may be considered. Japanese Patent No. 3507132 discloses measures against write failure in the event of an increase in the number of rewrites which is a drawback of flash memory. A storage system that has a built-in nonvolatile memory such as flash memory instead of or in addition to a HDD and stores data which are written to or read from the nonvolatile memory by a host by using the technology of Japanese Patent No. 3507132 may be considered. A storage device that combines an increase in the I/O processing speed with a reduction in the power consumed in comparison with a storage device that contains a disk device by storing host data in a nonvolatile memory can be provided. As a result, miniaturization of the system introduced and a reduction in the system running costs (the amount of power consumption) can be implemented. Flash memory, which constitutes the current mainstream form of nonvolatile memory, possesses low I/O performance in comparison with DRAM or S-RAM which are used for the main memory of computers. Furthermore, flash memory also possesses low input performance in comparison with HDD. Furthermore, flash memory also possesses the characteristic of adversely affecting user convenience (e.g. write count restrictions and so forth), hence, flash memory is adopted as a secondary storage device to substitute disk devices and so forth.
The first storage system shown in Japanese Application Laid Open No. 2005-11277 must contain a cache memory for the I/O processing of the second storage system which is an external storage system. Cache memory temporarily stores read or write target data when I/O processing is performed with respect to a disk device that the storage system contains, implements high-speed read and write processing using cache hits and is built into almost all storage systems. In this specification, a storage area that temporarily stores data as per cache memory is called a ‘temporary area’ and a storage area constituting the final storage destination for data as per a disk device is called as a ‘permanent area’.
In order to execute high-speed I/O with respect to an external storage system, a cache memory (temporary area) of the capacity required for I/O processing must be assigned to I/O processing in accordance with the capacity of the external storage system and access characteristic (locality) thereof.
Conventionally, a memory device such as a DRAM or SRAM has been adopted as the cache memory (temporary area) and has contributed toward increased storage system speeds as a storage medium that possesses completely different characteristics from a disk device (permanent area), which is termed ‘high cost, high-speed, and small capacity’. Conversely, in addition to a built-in disk device (permanent area) in the above first storage system, the inclusion of a memory device as a temporary area used for an external storage system (and an internal built-in disk device) in order to respond to the characteristics required of a temporary area has not been possible.
However, in cases where the first storage system comprising external storage connection means is a storage system that uses a nonvolatile memory as the permanent area, a nonvolatile memory can be used as a temporary area of the external storage in the same way as a permanent area. By using a nonvolatile memory as a temporary area or a permanent area, there is no longer a need to mount both a disk device and memory together and the hardware is simplified, whereby a reduction in hardware costs is possible. However, in this implementation, a management technology that is capable of determining and managing the capacity and locations of the temporary and permanent areas assigned in the nonvolatile memory is required in the implementation. In addition, a change to the temporary area assignment that satisfies the IO processing requirements of the external storage in accordance with an addition to or reduction in the external storage system as well as changes to the access characteristics is required.
In addition, in the next-generation nonvolatile memories such as MRAM and PRAM for which research is progressing as a future technology, the implementation of a high-speed characteristic that rivals that of DRAM or the like and the elimination of write limitations is planned and a new architecture will be necessary at the time such a new nonvolatile memory is introduced.